Gage control method and system for tandem rolling mills

ABSTRACT

Gage control method and system for tandem rolling mills of the type wherein final output gage is controlled by comparing actual output gage with desired output gage to develop an error signal for controlling the speed of the last stand and, hence, tension in the strip material being rolled between the last two stands. The invention is characterized in that the roll force exerted on the strip by the last stand is maintained constant for all variations in last stand speed, thereby enabling a greater range of strip gage change via the last stand in the tandem mill.

United States Patent n91 Connors CAGE CONTROL METHOD AND SYSTEM FOR TANDEM ROLLING MILLS [451 May 7,1974

Primary Exa miner-Milton S. Mehr Attorney, Agent, or Firm-Brodahl, R. G.

[ 5 7 ABSTRACT Gage control method and system for tandem rolling mills of the type wherein final output gage is controlled by comparing actual output gage with desired output gage to develop an error signal for controlling the speed of the last stand and, hence, tension in the strip material being rolled between the last two stands. The invention is characterized in that the roll force exerted on the strip by the last stand is maintained constant for all variations in last stand speed, thereby enabling a greater range of strip gage change via the last stand in the tandem mill.

7 Claims, 1 Drawing Figure s1 :e at 3. s5. 40 5; l0 l4 (g) g? g? 26 TI T2 T3 T4\ I MI M2 M3 M4 M5 HI H2 If? H3 H4 H5 @9 7 CI c2 03 r r r r r SPEED SPEED SPEED SPEED sPEEO .CONTROL CONTROL CONTROL CONTROL CONTROL T02 T63) T64) I CONSTANT GAGE TENSION TENSION TENSION ROLL CONTROL CONTROL CONTROL CONTROL FORCE CONTROL 24 l l I 2O- DESIRED TENSION GAGE "f 'if i TENSION ERROR I CONTROL CONTROLLER I i T I I DESIRED I SUMMER THICKNESS M I -1 TENSION COMPEN- I I SATION 4 GAGE CONTROL METHOD AND SYSTEM FOR TANDEM ROLLING MILLS BACKGROUND OF THE INVENTION In the past, it has been common to control the gage of strip material passing througha tandem rolling mill by adjusting the first stand screwdown while simultaneously controlling the interstand tension in the strip between succeeding stands. The final output gage on Inulti-standmills is most widely performed by means of tension variation between the last stand and the previous stand. in this respect, an X-ray thickness gage positioned beyond the bite of the rolls of the last stand measures actual output thickness which is then compared with desired, final thickness to derive an error signal for controlling 'the last stand speed. If the actual, measured thickness is above desired gage, for example, then the last stand speed is increased to increase the tension between the last two stands and reduce gage.

The final output gage can also be controlled by adjusting the last stand screwdown; however this method can interfere with strip shape and-is not nearly as fastacting as gage control by tension variation between the last two stands.

One outstanding limitation of control of final output gage in a tandem rolling mill by variation in tension between the last two stands is the inability of the tension change to vary strip gage more than 4 or 5 percent of nominal gage. This is due partly to the permissible range of tension variation, about 40 percent of the nominal value, and partly due to the characteristics of rolling. In this respect, and by reference to an article by William L. Roberts appearing in the Iron and Steel En-' The term l.l5 Gy is about constant for a hard strip and small variation in reductions. Furthermore,.it can be shown that:

and

where: v

'F= roll force; and

L effective length of the profile of contact. From the foregoing equation, it can be seen that as tension increases, the roll force must decrease. ln other words, as tensionacts to decrease gage, for example, the decrease in roll force acts against it and attempts to increase gage. This characteristic of rolling reduces the effectiveness of interstand tension regulation between the last two stands of a tandem rolling mill for final gage control.

SUMMARY OF THE INVENTION In accordance with the present invention, a final gage control system and method for a tandem rolling mill are provided wherein final gage is varied by varying tension in the strip material being rolled between the last two stands while the roll force exerted on the strip by the last stand is maintained constant for all variations in last stand speed to enable a greater range of final gage change.

Specifically, there is provided means for measuring the actual gage of the strip material issuing from the last stand and for producing a first electrical signal proportional thereto, together with means for comparing the first electrical signal witha second electrical signal proportional to the desired output gate to derive an error signal when the desired and actual gages are not the same. Circuitry is provided which is responsive to the error signal for varying the speed of the last stand to thereby vary tension between the last two stands and vary actual output gage until the desired and actual output gages are the same and the error signal is zero. Additionally, a load cell is provided on the last'stand which produces an electrical signal proportional to roll force exerted by the last stand. This latter electrical signal is then used to maintain, preferably through hydraulic cylinders, a'constant roll force on strip material passing through the last stand regardless of variations in tension between the last two stands.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with'the accompanying single FIGURE drawing which schematically illustrates one embodiment of the invention.

With reference now to the drawing, the system shown includes a five-stand tandem rolling mill including stands 81, S2, S3, S4 and S5. Each stand includes a pair of work rolls l0 and 12 between which strip material 14 being rolled passes, together with a pair of backup rolls l6 and 18. The stripissu'ing from the-last stand S5 is wound on a coiler 15. The rolls of each stand are driven by means of drive motors M1, M2, M3, M4 and M5 each controlled by speedcontrol circuits C1, C2,

C3, C4 and C5, respectively. The speed control circuits C1-C5, in turn, are connected to a master speed controller 20 which establishes a nominal or desired speed for each of the stands in the mill to achieve a desired gage reduction. In this respect, and since each of the stands in the mill is reducing the strip in thickness, the speed of the strip material issuing from any stand must be greater than that entering the stand in accordance with the constant volume principle. Accordingly, the speed of stand S2 must be greater than that of stand S]; the speed of stand S3 must be greater than that of stand S2, and so on the speed of stand S5 being greatest.

In the embodiment of the invention shown herein, the chocks supporting the rolls in each stand are loaded by means of hydraulic cylinders H1, H2, H3, 1-14 and H5, respectively. That is, the hydraulic cylinders Hl-HS provide the necessary roll force to reduce the strip 14 in thickness. It is, of course, possible to use mechanical screwdown mechanisms or a wedgetype control to effect somewhat the same results; however hydraulic cylinders are preferred because of their speed of operation.

The gage of the strip material passing through the first stand S1 is measured by means of an X-ray gage 22 or the like. Gage 22 produces an electrical signal proportional to the actual gage between stands S1 and S2; and this signal is applied to a gage control circuit 24 where it is compared with an electrical signal proportional to desired exit gage from stand S1. If the actual gage does not match the desired gage, then the gage control circuit, through appropriate hydraulic controls, either increases or decreases the pressure on cylinder H1 to increase or decrease theroll force and thereby vary the gage of material issuing from stand S1 until it matches the desired gage. Stand 81, however, is the only stand in the tandem mill whose roll force is varied as a function of output gage in the. embodiment of the invention shown herein.

Between successive ones of the stands are tensiometers T1, T2, T3 and T4 which measure tension in the strip material between each set of stands. The tensiometer T1, for example, measures the tension between stands S1 and S2 and produces an electrical signal proportional thereto. This tension signal from tensiometer T1 is compared with a reference signal in tension control circuit TC2; and if the two are not the same, then the tension control circuit, through appropriate hydraulic controls, not shown, varies the pressure exerted by cylinder H2 for stand S2. Similar tension control circuits TC3-TC5 are provided for stands S3-S5, respectively.

Let us assume, for example, that the tension between stands S1 and S2 decreases from the desired value. Under these circumstances, and after comparison of the actual tension signal with a reference signal, the tension control TC2'will decrease the pressure exerted by cylinder H2; whereupon the roll gap of stand S2 will increase until the desired tension is maintained. Similarly, an increase in tension will result in greater pressure exerted by the cylinder H2 and a smaller roll gap until the desired tension is again maintained.

ple, may simply comprise a potentiometer or the like.

The tension control circuit TCS, enclosed by broken lines, is shown in somewhat greater detail than the tension controllers for the preceding stands. The actual tension signal from tensiometer T4 between stands S4 and S5 is again compared with desired tension from circuit 32 in a tension error determining circuit 34. In this respect, the tension control system is similar to that of the preceding stands. However, there is a third signal introduced into the tension error by circuit 34; and this is the gage error signal derived from gage control circuit 28 which modifies the desired tension signal from circuit 32. Thus, even if the actual tension measured by tensiometer T4 should equal the desire tension, an error signal will be derived from circuit 34 if the actual output gage derived from X-ray gage 26 is not equal to the desired gage. The tension error signal from circuit 34 is then applied to a tension compensation circuit where strip cross-sectional area and strip speed compensation are introduced into the error signal. The output of the circuit 36 is then summed with the desired speed signal from master speed controller 20 in summer38. If the two are not the same, an error signal is applied to the speed control circuit C5 to vary the speed of stand S5.

Up to this point, the system described is more or less conventional. However, as was explained above, it is not possible to change the tension in the strip between In accordance with the present invention, a reduction in roll force on the last stand is prevented by means for maintaining the roll force constant at all times. This includes a load cell 40 on stand S5 which produces an electrical signal porportional to the actual roll force exerted by stand S5. This signal is compared in roll force control circuit 42 with a fixed roll force reference signal; and if the two are not the same, the circuit 42 acts through suitable hydraulic controls to either increase or decrease the pressure exerted by the cylinder H5 and, hence, increase or decrease the roll force exerted by stand S5. In this manner, the roll force on stand S5 is maintained constant at all times and does not vary with changes in strip tension between stands S4 and S5, thereby overcoming the foregoing disadvantages of prior art systems described above.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to thoseskilled in the art that various changes in form and arrangement-of parts may be made to suit requirements without departing from the spirit and scope of the invention.

What is claimed is:

1. In a multi-stand rollingmill for metal strip material wherein the final output gage of the material issuing from the mill is controlled by controlling tension between the last two stands in the mill; the combination of: V

means for measuring the actual gage of strip material issuing from the last stand in said mill and for producing a first electrical signal proportional thereto,

means for comparing saidfir st electrical signal with a second electrical signal proportional to desired output gage to derive an error signal when the desired and actual gages are not the same,

means responsive to said error signal for varying the speed of said last stand to thereby vary tension between the last two stands and vary actual output gage until the desired and actual output gages are the same and said error signal is zero, and

means for maintaining a constant roll force on strip material passing through said last stand regardless of variations in tension between the last two stands and regardless of the speed of the last stand.

2. The combination of claim 1 wherein roll force is exerted by said last stand through a hydraulic cylinder.

3. The combination of claim 2 including a load cell for measuring actual roll force exerted by said last stand and for producing an electrical signal proportional thereto, means for comparing said electrical signal proportionalto actual roll force with a reference electrical signal to thereby derive an error signal, and means responsive to said error signal for varying the pressure exerted by said hydraulic cylinder.

4. The combination of claim 1 including a tensiometer for measuring tension between strip material being rolled between the last two stands in said multistand mill, said tensiometer producing a third electrical signal proportional to actual tension between the last two stands, means for comparing said third electrical signal with a fourth electrical signal proportional to desired tension and with said error signal proportional to a deviation in output gage from a desired gage to derive a second error signal, and means for controlling the speed of said last stand as a function of the magnitude of said second error signal.

5. The combination of claim 4 including means for comparing said second error signal with a master speed signal for deriving a final error signal for controlling the speed of said last stand.

6. The combination of claim 5 wherein the roll gap on the first stand is controlled as-a function of the measured actual output gage from the first stand in the tan- 6 dem mill 7. In the method for rolling metal strip material in a 'multi-stand rolling mill wherein the final output gage of material issuing from the mill is controlled by controlling tension between the last two stands in the mill; the

steps of:

until the desired and actual output gages are the same and said error signal is zero, and maintaining a constant roll force on strip material passing through said last stand regardless of variations in tension between the last two stands and regardless of the speed of the last stand. 

1. In a multi-stand rolling mill for metal strip material wherein the final output gage of the material issuing from the mill is controlled by controlling tension between the last two stands in the mill; the combination of: means for measuring the actual gage of strip material issuing from the last stand in said mill and for producing a first electrical signal proportional thereto, means for comparing said first electrical signal with a second electrical signal proportional to desired output gage to derive an error signal when the desired and actual gages are not the same, means responsive to said error signal for varying the speed of said last stand to thereby vary tension between the last two stands and vary actual output gage until the desired and actual output gages are the same and said error signal is zero, and means for maintaining a constant roll force on strip material passing through said last stand regardless of variations in tension between the last two stands and regardless of the speed of the last stand.
 2. The combination of claim 1 wherein roll force is exerted by said last stand through a hydraulic cylinder.
 3. The combination of claim 2 including a load cell for measuring actual roll force exerted by said last stand and for producing an electrical signal proportional thereto, means for comparing said electrical signal proportional to actual roll force with a reference electrical signal to thereby derive an error signal, and means responsive to said error signal for varying the pressure exerted by said hydraulic cylinder.
 4. The combination of claim 1 including a tensiometer for measuring tension between strip material being rolled between the last two stands in said multistand mill, said tensiometer producing a third electrical signal proportional to actual tension between the last two stands, means for comparing said third electrical signal with a fourth electrical signal proportional to desired tension and with said error signal proportional to a deviation in output gage from a desired gage to derive a second error signal, and means for controlling the speed of said last stand as a function of the magnitude of said second error signal.
 5. The combination of claim 4 including means for comparing said second error signal with a master speed signal for deriving a final error signal for controlling the speed of said last stand.
 6. The combination of claim 5 wherein the roll gap on the first stand is controlled as a function of the measured actual output gage from the first stand in the tandem mill.
 7. In the method for rolling metal strip material in a multi-stand rolling mill wherein the final output gage of material issuing from the mill is controlled by controlling tension between the last two stands in the mill; the steps of: measuring the actual gage of strip material issuing from the last stand in said mill and for producing a first electrical signal proportional thereto, comparing said first Electrical signal with a second electrical signal proportional to desired output gage to derive an error signal when the desired and actual gages are not the same, varying the speed of said last stand as a function of said error signal to thereby vary tension between the last two stands and vary actual output gage until the desired and actual output gages are the same and said error signal is zero, and maintaining a constant roll force on strip material passing through said last stand regardless of variations in tension between the last two stands and regardless of the speed of the last stand. 